The principal goal of this proposal is to define the anatomical structures and neural activity that underlie the surface recorded Event Related Potentials (ERP) associated with sensory, motor and cognitive processes. These studies utilize unanesthetized, behaving old world monkeys (M. fascicularis), as the closest feasible model for human ERP. After surface mapping of the specific ERP under study, depth recordings are employed to localize the intracranial generators and to define through three- dimensional intracerebral mapping, the relationship between field potentials recorded in the immediate vicinity of the active structures and the surface recorded potentials, which usually represent composite activity from more than one structure. The neural processes within each active structure are further delineated by concurrent recording of field potentials and MUA from closely spaced electrodes, utilizing a moveable multicontact electrode of our own design. Local outward and inward neural transmembrane current flows are estimated from the field potential data, utilizing current source density analysis. Identification of active structures and delineation of regions of enhanced neural metabolism within the structures under electrophysiological analysis is achieved by 2-Deoxyglucose autoradiography prior to sacrifice of each animal. Efforts will be made to identify the neurotransmitters involved in generation of specific ERP features. The initial focus is on the role of GABA in intracortical inhibitory circuitry, employing localized intracortical injections of the GABA antagonist bicuculline. This endeavor will be facilitated by immunocytochemical examination of the distribution of specific neurotransmitters within the brain structures under elecrophysiologic study. Studies will focus on stimulus related laminar patterns of evoked response in striate and extrastriate visual cortex, cerebral activity associated with trained self-initiated hand movements and the potentials related to the performance of visual and auditory discrimination tasks.